THÔNG TIN TÀI LIỆU
VIETNAM NATIONAL UNIVERSITY, HANOI UNIVERSITY OF ENGINEERING AND TECHNOLOGY Nguyen Ngoc Viet FLUIDIC CHANNEL DETECTION SYSTEM USING A DIFFERENTIAL C4D STRUCTURE Branch : Electronics and Telecommunications Technology Major : Electronics Technology Code : 60520203 MASTER THESIS ELECTRONICS AND TELECOMMUNICATIONS TECHNOLOGY SUPERVISOR: Assoc Prof Dr Chu Duc Trinh HA NOI - 2015 Acknowledgements I would first like to express my sincere gratitude towards my research supervisor, Assoc Prof Dr Chu Duc Trinh, who has helped me throughout my research work The teacher was always by my side for interesting discussions and for giving some fruitful advice In addition, I would also like to thank T Chu Duc’s research group members from MEMS Laboratory for their valuable inputs towards my research And last but not least, I am grateful to the Faculty of Electronics and Telecommunications, UETVNU, Hanoi for their willingness to offer help and suggestions whenever needed Finally, I want to express the deepest gratitude to my family and my friends for their love and encouragements during my study Ha Noi, November 1st, 2015 Nguyen Ngoc Viet Declaration I certify that the research described in this dissertation has not already been submitted for any other degree I certify that to the best of my knowledge all sources used and any help received in the preparation of this dissertation has been acknowledged Ha Noi, November 1st, 2015 Nguyen Ngoc Viet Table of contents List of figures List of tables List of symbols and abbreviations Summary 10 Chapter INTRODUCTION 12 1.1 Background and Overview 12 1.2 Research Objectives 13 Chapter THEORY OF CAPACITIVE SENSOR 17 2.1 Capacitance 17 2.2 Dielectric constant 19 2.3 Capacitive sensor applications 19 2.3.1 Proximity sensor 20 2.3.2 Position sensor 21 2.3.3 Humidity sensor 22 2.3.4 Pressure sensor 22 2.3.5 Tilt sensors 23 2.4 Basic principles of C4D structure 23 2.5 Coplanar capacitive sensor in CMOS chip 26 Chapter DIFFERENTIAL C4D STRUCTURE FOR DETECTION OF OBJECT IN FLUIDIC CHANNEL 29 3.1 DC4D sensor for Conductive and Non-conductive Fluidic Channel 29 3.1.1 Design and operation 29 3.1.2 DC4D simulations for non-conductive fluidic channel 31 3.1.3 Modelling of DC4D for conductive fluidic channel 34 3.1.4 Fabrication and measurement setup 36 3.2 Developing DC4D sensor for microfluidic channel 37 Chapter RESULTS AND DISCUSSIONS 43 4.1 DC4D sensor system using U-shaped electrodes 43 4.1.1 DC4D for non-conductive fluidic channel 43 4.1.2 DC4D for conductive fluidic channel 47 4.2 DC4D sensor system using microelectrodes 52 Conclusions 56 References 57 List of figures Figure 2.1 Charged parallel plates separated by an insulating medium 17 Figure 2.2 Examples of C4D designs used mostly for conduct metric detection 24 Figure 2.3 Design of a single C4D structure: (a) excitation and pick-up electrodes; (b) The equivalent circuits 24 Figure 2.4 Electric field formed between positive and negative electrodes for different pitch lengths, (l1, l2 and l3) 26 Figure 2.5 Sensing possibilities to detect various characteristic of samples: (a) sensing density, (b) sensing distance, (c) sensing texture, (d) sensing moisture 27 Figure 2.6 A simplified diagram of a capacitive sensing based LoC 28 Figure 3.1 Block diagram design of the DC4D fluidic sensor 29 Figure 3.2 The DC4D based on three-electrode configuration; (b) The equivalent diagram 30 Figure 3.3 The interface of the structure simulation process using COMSOL Multiphysics 31 Figure 3.4 Simulated picture of the electric field norm when a plastic particle inside the fresh water channel 32 Figure 3.5 Simulated picture of the electric field norm when a tin particle inside oil channel 33 Figure 3.6 Capacitance change versus particle position inside a single C4D 34 Figure 3.7 The equivalent circuit of the DC4D for conductive fluidic channel The circuit diagram of the suggested structure 35 Figure 3.8 The equivalent circuit of the DC4D fluidic sensor 35 Figure 3.9 The single C4D admittance change when a particle moves though electrode inside conductivity solution 36 Figure 3.10 Measurement system setup of the DC4D fluidic sensor 37 Figure 3.11 Proposal of a DC4D sensor 38 Figure 3.12 Cross-sessional view (a), side view (b), and DC4D sensor model (c) 39 Figure 3.13 Fabrication process 40 Figure 3.14 The fabricated chip 41 Figure 3.15 Block diagram of the measurement system 42 Figure 4.1 Capacitance change versus particle position inside a single C4D, when the air bubble and tin particle move through machine oil channel, respectively 43 Figure 4.2 Single C4D capacitance change versus volume of the particles in oil channel 44 Figure 4.3 The DC4D output voltage when a 4.18 l air bubble crosses electrodes in machine oil channel 45 Figure 4.4 The DC4D output voltage when a 4.18 l tin particle crosses electrodes in machine oil channel 45 Figure 4.5 The DC4D capacitance change when a 4.18 l air bubble crosses electrodes in machine oil channel 46 Figure 4.6 The DC4D capacitance change when a 4.18 l tin particle crosses electrodes in machine oil channel 46 Figure 4.7 The DC4D output voltage response versus tin particle volume in oil channel 47 Figure 4.8 The DC4D output capacitance change versus tin particle volume in oil channel 47 Figure 4.9 The DC4D output voltage response when a plastic particle crosses electrodes: (a) water channel; and (b) salt solution channel 48 Figure 4.10 The DC4D admittance change when a plastic particle crosses electrodes: (a) water channel; and (b) salt solution channel 48 Figure 4.11 The DC4D output voltage amplitude versus particle volume in salt solution and water 49 Figure 4.12 The DC4D output voltage amplitude versus particle volume in various concentration of salt solution 50 Figure 4.13 The DC4D output voltage change’s amplitude versus conductive fluidic resistivity 51 Figure 4.14 Velocity of investigated particle inside fluidic channel calculation 51 Figure 4.15 Meshed region 52 Figure 4.16 Capacitance output of the DC4D sensor 53 Figure 4.17 Maximum differential capacitance output versus particle’s volume 54 Figure 4.18 Maximum differential capacitance output and electrical field distribution in 3e positions of object inside water fresh flow: (a), (b), (c): air bubble; (d), (e), (f): tin particle 55 List of tables Table 3.1 Geometry parameters of the proposed DC4D structure 31 Table 3.2 Parameters of capacitive fluidic microsensor 38 Table 4.1 The DC4D output voltage amplitude versus particle volume in salt solution and water 49 Table 4.2 The DC4D output voltage amplitude versus particle volume in various concentration of salt solution 50 List of symbols and abbreviations C4D : Capacitively Coupled Contactless Conductivity Detection (or C4D) C0 : Stray capacitance (F) Cs : Solution capacitance (F) Cw : Wall capacitance (F) CMOS: Complementary Metal-Oxide-Semiconductor CTCs : Circulating Tumor Cells DC4D : Differential Capacitively Coupled Contactless Conductivity Detection di : Size parameters of the pipe (i=1,2,3) (m) E : Electric field intensity (V/m) f : Ordinary frequency (Hz) FEM : Finite Element Method Gs : Solution conductance (S) g : Gap of adjacent electrodes (m) h : Micro-channel’s height (m) LoC : Lab on Chip Li , li : Size parameters of the electrodes (i=1,2,3) MEMS: Micro Electro-Mechanical Systems PCB : Printed Circuit Board PDMS : Polydimethylsiloxane Q : Magnitude of charge (C) Rs : Solution resistance (Ω) V : Voltage applied (V) w : Electrode’s width (m) Z : Equivalent impedance (Ω) : Relative permittivity (dielectric constant) : Admittance constant : Angular frequency (rad/s) Summary Detection of the presence of strange particles in fluidic channels is important, due to their potential in chemical analysis, biology, pharmacology and especially in medical The appearance of air bubble in the patient’s blood vessels is dangerous in case of the unpredictable of cerebral embolism can lead to instant death The detection of strange cell in the blood vessel plays a crucial role in diagnosis or early detection of some diseases including cancer In MEMS, the appearance of a particle in the microfluidic channel can affect significantly to the response of the flow such as the flow velocity, the fluidic pure quality Among the different physical techniques for detection of objects in fluidic channel such as optical, ultrasonic, electrical sensing based on contact and contactless mechanism, capacitive sensing emerged as the best technique Capacitive sensor has been developed and applied in many field of technology due to simple fabricate and setup measurement, as well as minimization capability Additionally, there are many advantages of capacitive sensors in micro fabrication and integration on systems Capacitively coupled contactless conductivity detection (C4D) is a new detection technique has been developed in recent years and used mainly in capillary electrophoresis and microchip electrophoresis The characteristics of C4D detector are simple in structure, easy in miniaturization and integration, and free of electrodes contamination, which are common problems in an electrochemical detection This thesis presents a novel design of a differential C4D (DC4D) structure based on three U-shaped electrodes which can apply to the fluidic channel detection systems at millimeter size This structure consists of two single C4D with an applied carrier sinusoidal signal to the center electrode as the excitation electrode The electrodes are directly bonded on the PCB with built-in differential amplifier and signal processing circuit in order to reduce the parasitic component and common noise The proposed structure can be used for both conductive and non-conductive fluidic channel Simulations and experimental measurements are performed Experimental results show that a good agreement with the simulation Air bubbles and tin particles are pumped through electrodes for characterizing non-conductive fluidic case Plastic particles with various sizes are employed in the conductive fluidic configuration Changes in both particles position and volume result in changes in the capacitance, the admittance or the output voltage between the electrodes are investigated In the nonconductive fluidic channel, the output voltage and capacitance changes 214.39 mV 10 volume Therefore, this proposed DC4D sensor allows estimating the size of particle Output Voltage Change - mV when particle material is known 300 250 200 150 100 50 Measured data Linear fitted Volume - l Figure 4.7 The DC4D output voltage response versus tin particle volume in oil channel 20 C - fF 15 10 Measured data Linear fitted 0 Particle Volume - l Figure 4.8 The DC4D output capacitance change versus tin particle volume in oil channel 4.1.2 DC4D for conductive fluidic channel Figure 4.9 shows output voltage of the DC4D system when a plastic particle cross electrodes in salt solution and water channel as the investigated conductive fluidic The output voltage consists of both negative and positive peaks thank to the differential circuit The output voltage magnitude changes up to 300 mV and 50 mV when a 4.88 l plastic particle cross electrodes in water channel and plastic particle 47 cross electrode in salt solution channel, respectively Figure 4.10 shows admittance change of DC4D sensor when a plastic particle crosses water and salt solution The result is approximately matching with the calculated value Output voltage - V 1.7 1.6 1.5 1.4 1.3 Particle in water Particle in NaCl 1.2 Time - s Figure 4.9 The DC4D output voltage response when a plastic particle crosses electrodes: (a) water channel; and (b) salt solution channel x 10 -8 Admittance change - S -2 -4 Particle in water Particle in NaCl -6 -8 Time - s Figure 4.10 The DC4D admittance change when a plastic particle crosses electrodes: (a) water channel; and (b) salt solution channel 48 Table 4.1 The DC4D output voltage amplitude versus particle volume in salt solution and water Output voltage amplitude (mV) Plastic particle volume (µl) Salt solution 0.9% Fresh water 1.5 25 142 4.63 115 650 4.88 140 700 5.87 155 800 6.25 180 897 9.37 220 1200 Table 4.1 and Figure 4.11 show the relation between output voltage amplitude versus volume of plastic particle in 0.9% salt solution and water It shows that the relations are linear and output voltage in water channel is about times larger than the 0.9% salt solution case 1500 Voltage output - mV salt solution Linear fitted water 1000 500 0 10 Volume - l Figure 4.11 The DC4D output voltage amplitude versus particle volume in salt solution and water The proposed DC4D sensor is also characterized in various concentration of salt solution Table 4.2 and Figure 4.12 shows the relation between output voltage amplitude and investigated plastic particle volume in salt solution It shows that the 49 sensitivity of the sensor reduces when salt concentration in solution is increased The conductivity of the fluidic can be estimated by using this configuration when volume of the particle is known Table 4.2 The DC4D output voltage amplitude versus particle volume in various concentration of salt solution Output voltage amplitude (mV) 0.75% 0.9% 1.5% 35 25 16 130 110 68 150 115 75 165 140 76 180 155 95 186 180 117 288 220 152 Plastic particle volume (µl) 1.5 4.25 4.63 4.88 5.87 6.25 9.37 3% 10 36 37 45 47 60 78 300 salt solution 0.75% salt solution 0.9% salt solution 1.5% salt solution 3% Linear fitted 250 Delta V - mV 200 150 100 50 0 10 Particle volume - l Figure 4.12 The DC4D output voltage amplitude versus particle volume in various concentration of salt solution Figure 4.13 shows output voltage amplitude change versus conductive fluidic resistivity when a 9.37 µl particle moves through the sensor The relation is linear with sensitivity of about 400 mV/.m Therefore, this DC4D sensor can be used for measurement the fluid sensitivity when volume of particle is known In practice, a controlled air bubble pump can be added before sensor inlet for the fluidic sensitivity detector 50 250 DeltaV - mV 200 150 100 50 Measured data Linear fitted 0 0.1 0.2 0.3 0.4 0.5 0.6 Resistivity - .m Figure 4.13 The DC4D output voltage change’s amplitude versus conductive fluidic resistivity A B 14 mm 1.8 B Output voltage - V 1.7 1.6 1.5 1.4 1.3 1.2 A 0.5 1.45 (s) 1.5 2.02 (s) 2.5 3.5 Time - s Figure 4.14 Velocity of investigated particle inside fluidic channel calculation Figure 4.14 shows output voltage signal and the electrodes layout in this proposed DC4D fluidic sensor for particle velocity detection The two voltage picks are corresponded to the A and B point, which are center of each single C 4D structure, respectively Therefore, particle velocity can be extracted from distance AB divided by the time between the two voltage picks 51 In summary, the proposed DC4D sensor can be used for both conductive and non-conductive fluidic channel Air bubbles and tin particles are pumped through electrodes for characterizing non-conductive fluidic case Plastic particles with various sizes are employed in the conductive fluidic configuration The measured results indicated the linear relation between output voltage and volume of the particle Beside particle detection, this sensor allows measuring velocity of the particle inside fluidic channel thanks to distance and travel time between the two single C4D structure This DC4D fluidic sensor can be used for two-phase flow detection in petroleum industry, particle in fluidic channel detection and living cell in micro vessel detection and counting for biomedical applications 4.2 DC4D sensor system using microelectrodes Micro object Micro channel Figure 4.15 Meshed region FEM simulations were continued to perform using the COMSOL Multiphysics AC/DC module In which, the complex Laplace equation was used to solve for the electric fields in the microchannel In order to analyze problem, the domain is split into smaller sub domains, which is called mesh generation The mesh used is shown in Figure 4.15 Before the simulation can be run, specific parameters and boundary conditions had to be set, such as the radius of object, material properties, electrical terminals… 52 The simulation results from particles in the fresh water channel are provided in Figure 4.16 It shows that the maximum change of capacitance between electrodes is nearly 0.375 fF when a 30 µm diameter tin particle moving in the fresh water channel Meanwhile, the change is about 0.5 fF in case of air bubble with same diameter In both cases, we observe a decrease in capacitance because the dielectric constants of both air bubble ( r ) and tin particle ( r 24 ) are less than that of water ( r 81 ) The larger capacitance change from air bubble compared with tin particle occurs because the air bubble have a less permittivity compared with tin particle Therefore, the electrical property of the object can be estimated through the output signal Figure 4.16 Capacitance output of the DC4D sensor In addition, air bubble and tin particle objects in fresh water channel, with different diameter variables from 10 to 36 µm air also implemented The diameters correspond to the volume varies from 0.005 to 0.05 nl The sensing capacitance changes, when each particle is the center of the single C4D structure, are shown in 53 Figure 4.17 As can be seen, the relations between the output capacitance and the volume of the corresponding object are also linear The line angle is about -15 fF/nl with respect to the tin particle and -30 fF/nl with respect to the air bubble Moreover, the capacitance change of sensor in case of air bubble is higher than in case of tin particle Figure 4.17 Maximum differential capacitance output versus particle’s volume Figure 4.18 presents the electrical field profile of a cross section of the microfluidic flow with the appearance of tin and air bubble corresponding to different positions inside the channel The figure also shows that the maximum capacitance change of sensor gets the highest value in case of corner position for air bubble object and center position for tin object inside the channel The air material has non-conductive property, so the electrical distribution inside the spherical object is non-uniform as shown by color in the figure In contrast with air bubble material, the electrical distribution is uniform in the tin object The sensing chip has been manufactured successfully Besides, the measuring circuit is currently being edited and improved by our research team Therefore, the experimental measurement for this 54 micro-system will be installed and implemented in the near future Measurement results will be compared with corresponding simulation results and discussed later Microchannel Object (a) ΔC= 0.510 fF (d) ΔC= 0.364 fF (b) ΔC= 0.133 fF (e) ΔC= 0.122 fF (c) ΔC= 0.132 fF (f) ΔC= 0.121 fF Figure 4.18 Maximum differential capacitance output and electrical field distribution in 3e positions of object inside water fresh flow: (a), (b), (c): air bubble; (d), (e), (f): tin particle 55 Conclusions This thesis presents a DC4D structure which can apply to the fluidic channel detection systems The proposed structure can be used for both conductive and nonconductive fluidic channel at millimeter size Air bubbles and tin particles are pumped through electrodes for characterizing non-conductive fluidic configuration Plastic particles with various sizes are employed in the conductive fluidic case The system was simulated and fabricated Experimental measured results show that a good agreement with the simulation In the non-conductive fluidic channel, the output voltage changes about 25 mV and 200 mV, when a 4.18 µl air bubble and tin particle crosses an oil channel, respectively Meanwhile, the output capacitance changes about fF and 14 fF with respect to air bubble and tin particle In conductive fluidic channel, the output voltage and admittance changes up to 300 mV and 0.07 µS for the movement of a 4.18 µl plastic particle through channel The results indicated the linear relation between output voltage and volume of the particle Beside particle detection, this sensor system allows measuring velocity of the particle inside fluidic channel thanks to distance and travel time between the two single C4D structure A microsensor based on DC4D structure is also designed, simulated and fabricated The four-electrode capacitor is covered by thin PDMS protective layer Capacitive sensor structure is made of gold on glass substrate The output capacitance changes versus air bubble, tin particle object’s volume and position are simulated by using FEM tools The simulation inspection reveals that the sensor can detect an object with diameter from 10 µm to 40 µm in a 50×100 µm cross-section channel, with capacitance changes up to fF The DC4D microsensor is also fabricated by micro machining A measurement setup was designed and implemented to monitor the capacitance change The measurement with particle and living 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Method”, Electromechanical science 61 ... setup measurement, as well as minimization capability Additionally, there are many advantages of capacitive sensors in micro fabrication and integration on systems Capacitively coupled contactless... output signal of measurement device 16 Chapter THEORY OF CAPACITIVE SENSOR 2.1 Capacitance Capacitance is the important electrical property of capacitors Capacitance is measured in Farad (F), and it... conductivity detection, abbreviated as C4D, which was proposed by Fracassi da Silva, et al and Zemann, et al., independently in 1998 [1, 19], as a detection technique for capillary electrophoretic systems
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